The invention relates to optical devices that use specular reflection. More specifically, this invention relates to micro-devices that modulate light through specular reflection.
Specular reflection is used in a number of micro-machine devices with mirror structures for modulating and directing light beams. For example, micro-machine devices with mirror structures are used for optical switches. Grating light valves have several mirror structures that are selectively moved to modulate an incident light beam. Grating light valves have applications in display, print, optical and electrical technologies.
Grating light valves are micro-fabricated from Si-based materials using lithographic and etching techniques. Grating light valves are configured to have a plurality of ribbon structures which are selectively moved by applying an operating bias voltage across the ribbons and a substrate structure coupled to the ribbon structures. The top surfaces of the ribbon structures, and in some instances the top surfaces of the substrate, are provided with a thin reflective coating or layer such as an aluminum layer. The reflectivity of layer or coating tends to degrade after prolonged exposure to an intense light source, thereby limiting the applications where such devices can be used.
It is likely that the observed degradation in reflectivity of the ribbon structures is the result of thermal gradients induced by the small amounts of absorbed light.
Accordingly, to reduce the observed degradation of the reflective surfaces, grating light valves are required to be cooled when used in applications which require that the ribbons experience prolonged exposure to an intense light source. This requires that the device or the system has a cooling mechanism, such as a refrigerator compressor and a circulator. What is needed is a micro-machine with a mirror structure which exhibits consistent reflectivity to prolonged exposure to light. Further, what is needed is a grating light valve with a plurality of reflective ribbon structures which do not exhibit substantial degradation with prolonged exposure to an intense light sources such as laser light source.
The current invention is directed to optical devices and systems with surfaces for providing specular reflection. More specifically, the invention is directed to micro-structures which modulate or direct a light beam through specular reflection. In accordance with the instant invention, the micro-structure has a patterned reflective surface. The reflective surface is patterned with primary reflective regions formed from a reflective material. The primary reflective regions are separated by gap regions. The reflective surface is patterned to reduce thermal gradient induced atomic flux or atomic migration of the reflective material. Accordingly, patterned reflective surfaces show reduced degradation in reflectivity with prolonged exposure to an intense light source. The micro-device is preferably configured to modulate a light beam by controllably moving the micro-structure relative to the light beam.
The micro-structure can have any number of irregular or regular shapes, including a square or circular shape. The micro-structure is preferably an elongated ribbon structure with a substantially constant width in an active portion of the ribbon structure. The ribbon structure is preferably one of a plurality of ribbon structures within a grating light valve or a micro-electrical mechanical system (MEMS).
The ribbon structure preferably has a length in a range of 50 to 1000 microns and a width in a range of 1.0 to 10.0 microns. The ribbon structure is preferably formed from a Si-based material such as Si, SiO2, Si3N4 or combination thereof. The ribbon structure is formed using lithographic etching techniques or any other suitable method. The ribbon structure is provided with a patterned reflective surface in the active portion of the ribbon. Preferably, the patterned reflective surface has a segmented pattern, wherein the reflective surface has primary reflective regions separated by linear gap regions.
In accordance with the preferred method of the instant invention, the ribbon structure is provided with a patterned reflective surface by depositing a continuous layer of a reflective material on the surface of a ribbon element and then patterning the layer to form the primary reflective regions and the gap regions. Alternatively, the reflective material is selectively deposited on the surface of a ribbon element to form the reflective regions through a positive or negative mask. The reflective material is preferably a reflective metal, which may be platinum or an alloy thereof.
The reflective regions are preferably 3.0 to 30 microns along the length of the ribbon structure. The primary reflective regions are approximately equal in size and area. Alternatively, the primary reflective regions are varied in size and area. The gap regions are preferably between 0.1 and 2.0 microns along the length of the ribbon. The gap regions are approximately of equal size and area. Alternatively, the gap regions are varied in size and area. Further, the distribution of primary reflective regions and gap regions is symmetric or asymmetric along the length of the ribbon. Preferably, the gap regions account for 10% or less of the total surface area corresponding to the active portion of the ribbon structure. Also, the gap regions preferably extend across the entire width of the ribbon structure to completely isolate the reflective material within primary reflective regions from the reflective material within adjacent primary reflective regions.
In accordance with the instant invention, the gap regions are formed from any number of materials which reduce flux or migration of atomic species between adjacent reflective regions. It is believed that heterogenous interfaces as well as spaces between adjacent primary reflective regions mitigate or reduce atomic flux or migration which can ultimately lead to the degradation of the thin reflective. Accordingly, the gap regions are left vacant and have exposed Si-based ribbon layer or, alternatively, the gaps are coated or filled with a second material. The second material is a different material from the reflective material used to form the primary reflective regions. The second material is a non-reflective material, a reflective material or semi-reflective material. In a preferred embodiment, the gap regions are provided with a high melting point metal such as platinum.
A grating light valve, in accordance with the instant invention, has a plurality of ribbon structures patterned or segmented as described above. A selected portion of the ribbons are configured to move by a distance n(xcex/4) to modulate a light source having a wavelength xcex. Preferably, the selected portion of the ribbons are selectively moved by applying an alternating bias voltage across the selected ribbons and a substrate couple to the ribbons.